Mickey Rourke in 'Sin City: A Dame to Kill For.' The film finished in eighth place at the box office, with a $6.5 million opening weekend. / Weinstein/Dimension

by Scott Bowles, USA TODAY

by Scott Bowles, USA TODAY

Sin City committed one of Hollywood's deadliest this weekend: boring moviegoers.

The result was one of the higher-profile Hollywood flops of the summer. Sin City: A Dame to Kill For, the sequel to the 2005 fanboy favorite, mustered just $6.5 million and eighth place, according to studio estimates from Rentrak.

The opening fell well below expectations, with analysts having anticipated a No. 1 debut of at least $15 million.

But mixed reviews and weak word-of-mouth undercut the movie, whose stars include Josh Brolin and Jessica Alba, leaving the top spot up for grabs between a new young-adult film and superhero holdovers.

The holdovers won out as Guardians of the Galaxy reclaimed the No. 1 position with $17.6 million. The film has done $251.9 million since its Aug. 1 release, making it summer's biggest hit.

It proved a stronger reception than Dame's. Though the movie earned an approval rating of 43% of critics, it scored just a "B-" with fans, says CinemaScore, an ominous sign for its long-term prospects.

"The big story of the week is" not the box-office race, suggest David Mumpower, analyst for Box Office Prophets. "Instead, it is the shocking failure of Sin City: A Dame to Kill For, which would have been more aptly titled A Dame to Ignore."

Mumpower notes that the original film directed by Frank Miller and Robert Rodriguez became a crime noir hit, collecting an unexpected $74 million, and says a sequel should have arrived sooner.

Dame "has been released half a dozen years too late for anyone to care," he says. "Because of this inexplicable delay, a project that easily could have opened to $50 million in 2007" couldn't crack the top five.

The comedy Let's Be Cops was fourth with $11 million.

Sports drama When the Game Stands Tall met most projections, rounding out the top five with $9.1 million.